There appears to be some confused thinking at another discussion forum about the DNA profile associated with the knife. Let me try to summarize the debate.
Dr. Elizabeth Johnson said as reported by ABC’s Ann Wise on 1 December 2009, “if someone had a knife covered in blood and they tried to clean it very well, they would remove their ability to detect the DNA before they removed the ability to detect the chemical traces of blood.” Note that this statement is made about DNA, not DNA from any one particular cell type. If it is true, it rules out the possibility that the DNA arose from the murder.
The profile that Dr. Stefanoni conjured up is an imperfect but good representation of Meredith’s DNA profile. We are left with four possibilities as to how it arose. 1. Secondary transfer, as discussed by Dr. Kekule, for example. 2. Contamination when it was being taken into evidence. 3a. Contamination in the lab due to handling of the knife. 3b. Contamination in the lab due to DNA in the reagents or in the electrophoresis apparatus. 4. Evidence tampering. The only one of these possibilities in which there is never DNA on the knife is 3b. However, possibilities 2, 3a, and 4 mean that there was no DNA on the knife until ILE handled it. The distinction between “never” and “only after ILE has custody” may be important in some discussions and unimportant in others. The large amount of Meredith’s DNA in the lab could have been deposited on the knife directly (3a) or found its way into the reagents or apparatus (3b).
With respect to the bra clasp profile, The Machine at Perugia Murder File wrote, “Sollecito's DNA on Meredith's bra clasp was LCN DNA despite the fact that the lowest RFU peak was 30% higher than that the 50 RFU test widely used for minimum reliability and the highest RFU peak was more than 200% higher.”
I find it interesting that The Machine would place so much stock in the 50 RFU threshold. 22 of 29 peaks in the knife profile fall below this value. The Machine should explain why this threshold is important for the bra clasp but can be ignored for the knife.
Finally, The Machine quoted Mr. Maresca (attorney for the Kercher's) as saying that the tests are indisputable, “All tests are not disputable, since all attorneys and their consultants were notified on the time and date of these non-repetitive tests”. This is problematic on at least two fronts. The first is that Mr. Maresca and Mr. Mignini were essentially on the same team, as I documented upthread. The second is that Mr. Maresca is ignoring the fact that LCN testing needs to be done at least twice, preferably more, and preferably with enough sample left over for the defense. This is the same anonymous commenter who could not find a single case of credible forensic DNA contamination, despite the wide availability of information on this subject.
